Alkene

An alkene in organic chemistry is an unsaturated hydrocarbon containing at least one carbon to carbon double bond. The simplest alkenes, with only one double bond, form a homologous series, the alkenes with general formula CnH2n.

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The simplest alkene is C2H4, which has the common name "ethylene" and the International Union of Pure and Applied Chemistry (IUPAC) name "ethene". Alkenes are also called olefins and vinyl compounds.

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Shape of Alkenes

As predicted by the VSEPR model of electron pair replusion, in the molecular geometry of alkenes the bond angles about each carbon in a double bond are about 120°, although the angle may be larger because of steric strain introduced by nonbonded interactions created by functional groups attached to the carbons of the double bond. For example, the C-C-C bond angle in propene is 123.9°. The alkene double bond is stronger than a single covalent bond and also shorter with an average bond length of 133 picometer.

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Molecular Geometry

Like single covalent bonds, double bonds can be described in terms of overlapping atomic orbitals, except that unlike a single bond (which consist of a single sigma bond), a carbon-carbon double bond consists of one sigma bond and one pi bond.

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Each carbon of the double bond uses its three sp2 hybrid orbitals to form sigma bonds to three atoms. The unhybridized 2p atomic orbitals, which lie perpendicular to the plane created by the axes of the three sp2 hybrid orbitals, combine to form the pi bond.

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Because it requires a large amount of energy to break a pi bond (264 kJ/mol in ethylene), rotation about the carbon-carbon double bond is very difficult and therefore severely restricted. As a consequence substituted alkenes exist as one of two isomers called a cis isomer and a trans isomer. In cis-2-butene two methyl substituents face the same side of the double bond and in trans-2-butene they face the opposite site.

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Organic chemistry: Organic chemistry is the scientific study of the structure, properties, composition, reactions, and synthesis of organic compounds that by definition contain carbon. It is a specific discipline within the subject of chemistry. Organic compounds are molecules composed of carbon and hydrogen, and ma...

Unsaturated: REDIRECT Saturation...

Carbon: :Alternative meaning: Carbon (API)...